Generally, a high-voltage DC circuit breaker is a switching device that may break a current flowing through a high-voltage transmission line for 50 kV or more, such as a High-Voltage Direct Current (HVDC) transmission system. Such a high-voltage DC circuit breaker serves to break a fault current when a fault occurs in a DC line. Of course, it may also be applied to an intermediate voltage DC distribution system for a DC voltage level that ranges approximately from 1 to 50 kV.
When a fault current occurs in a system, the high-voltage DC circuit breaker opens a main switch so as to disconnect the circuit in which a fault occurs, whereby the fault current is interrupted. However, because there is no zero current point in a DC line, an arc, generated across the terminals of a main switch when the main switch is opened, is not extinguished. Accordingly, the fault current continuously flows through the arc, and thus the fault current cannot be interrupted.
In order to break a fault current by extinguishing an arc generated when opening a main switch CB in a high-voltage DC circuit breaker, Japanese Patent Application Publication No. 1984-068128, illustrated in FIG. 1, provides a technique in which the arc is extinguished by a zero current at the main switch CB, which is formed by superposing a resonance current Ip, generated by an LC circuit, onto a current IDC that flows in a DC line (Idc=IDC+Ip). Specifically, if an auxiliary switch S is closed when the main switch CB is open and an arc is generated, a positive (+) resonance current (Ip>0) is applied to be superposed onto the DC current IDC. Then, the resonance current Ip oscillates between positive (+) and negative (−) values due to the resonance between L and C, and the magnitude thereof increases as the oscillation is repeated along the main switch CB. Accordingly, when the magnitude of the negative (+) resonance current (Ip<0) becomes the same as that of IDC, the current Idc becomes a zero current, and the arc of the main switch CB is extinguished. However, according to this conventional art, because it is necessary to superpose the positive (+) resonance current Ip, which is equal to or greater than the DC current IDC, a circuit rating should be more than two times of that of a rated current. Also, in order to realize such a large resonance current Ip, multiple resonance cycles are necessary, and thus the breaking speed is decreased. Also, the conventional DC circuit breaker has a problem that it cannot interrupt a bidirectional fault current.